Two-Dimensional Arrays: Arrange Data in a Grid

Think together · Start with a story

A girl finds a classmate by asking, “Which row and which seat?” That is how she locates an item in a table.

Break down the process

Follow the numbered steps, then explain them in your own words

A two-dimensional array can be understood as a table made of rows and columns.

Some data naturally has rows and columns, such as a seating chart, a game board, or a table of values.

int a[2][3];

This declares 2 rows with 3 integers in each row.

The first index selects the row, and the second selects the column. Since indexes start at 0, a[1][2] means the second row and third column.

Row and column indexes both start at 0.

In C++:

int a[2][3];

You can think of a as an array of length 2, where each element is itself an array of 3 integers.

An ordinary two-dimensional array is stored in contiguous row order:

a[0][0]→a[0][1]→a[0][2]→a[1][0]→...

This is commonly called row-major order.

for (int row = 0; row < 2; row++) {
    for (int col = 0; col < 3; col++) {
        std::cout << a[row][col] << ' ';
    }
}

The outer loop controls the rows; the inner loop controls the columns.

Of course. For int a[2][3]:

Both a[2][0] and a[0][3] are out of bounds.

Next: What Is a String?

For an array with 2 rows and 3 columns, is a[2][0] valid?

Ready? Open to see the explanation

No. The row index can only be 0 or 1. A valid column index cannot make an out-of-bounds row valid.